Microemulsions are useful as compositions that combine the solvency or other desired activity of a solvent or oil phase with the detergency or other desired activity of the surfactants and other components of an aqueous phase. They are optically clear, thermodynamically stable compositions typically comprising water insoluble or sparingly soluble liquid solvents or oils, surfactants or mixtures thereof, various cosurfactants, and water. The cosurfactants can be low molecular weight alcohols containing 2 to 10 carbon atoms, mono or polyglycols, glycol ethers, cyclic ketones, and the like. The purpose of adding the cosurfactants to the formulations is to decrease the interfacial tension between the aqueous phase and the insoluble solvent or oil phase so that the composition becomes a thermodynamically stable mixture of bicontinuous phases. These cosurfactants typically have moderate to high volatility, which may add to the volatile organic compound (VOC) content of formulations and thus may restrict their applications, and also may add distinctive and often objectionable odors. The microemulsion formulations may also contain other components such as detergent builders, alkalies, viscosifying agents, dyes and perfumes commonly found in detergent formulations.
Many microemulsion compositions are known. Examples include U.S. Pat. Nos. 6,824,623, 6,244,685, 5,990,072, and 5,952,287, which describe compositions containing alkyl esters as the oil phase, and various surfactants and other ingredients, all requiring the use of a cosurfactant. Further examples are U.S. Pat. Nos. 5,717,925, 5,616,548, 5,108,643, 5,082,584, and WO2004/07887, which describe microemulsions with a range of insoluble oils and surfactant systems. These compositions and other compositions of the prior art require the use of cosurfactants in their formulation.
Ethoxylated amines and ethoxylated quaternary ammonium salts have been shown to have detergent properties in specific applications, and are occasionally used in detergent compositions. Ethoxylated amines are described in U.S. Pat. Nos. 6,080,713, 5,719,118, and 5,616,811, incorporated herein by reference.
Fatty acid soaps usually derived from natural oils and fats have been widely used as surfactants in detergent and cleaner formulations since antiquity. Soaps of oleic and linoleic acid have been shown to have utility in forming microemulsions, for example in U.S. Pat. No. 5,990,072. They require the use of a cosurfactant to form clear microemulsions.
The use of mixtures of anionic and cationic surfactants is usually avoided because the mixtures tend to form precipitates in aqueous systems. However, it is known that these mixtures may have beneficial surfactant properties if they are properly formulated, due to the property of having very low surface and interfacial tension. U.S. Pat. No. 6,617,303 describes mixtures of ethoxylated fatty amines with anionic surfactants, including ether carboxylates. GB Patent No. 2,195,653 describes complexes of ethoxylated amines and higher alkyl fatty acids as emulsifiers for fabric softener quaternary ammonium salt-anionic surfactant complexes. U.S. Pat. No. 5,622,554 describes asphalt compositions containing ether amine salts of carboxylic acids. U.S. Pat. No. 6,169,064 describes mixtures of alkyl polyether carboxylates and ether arnines or alkyl amines. U.S. Pat. No. 4,472,291 discloses microemulsions formed from charged primary surfactants, cosurfactants, and a secondary surfactant that is oppositely but not highly charged, added to increase the viscosity. EP Patent No. 0160762 discloses microemulsion compositions wherein a nitrogen-containing compound is added to a fatty acid soap containing formulation to provide pH stability. U.S. Pat. No. 5,298,193 describes mixtures of nonionic surfactants with an anionic surfactant and a cationic surfactant. In the '193 patent alkoxylated amines are described as nonionic surfactants, and can be used to stabilize the anionic-cationic complexes.
Mixtures of ethoxylated tallow amine and branched acids are disclosed in U.S. Pat. Nos. 5,945,026, 6,139,775, 6,740,250, and US Pub. No. 2003/001057. These compositions contain cosurfactant alcohols and are used as concentrates for firefighting solutions.
Mixtures of saturated carboxylic acids, which may be branched, and ether amines are disclosed in US Pub. No. 2004/0010967. They are useful as friction modifiers for combustible fuels.
It is an object of this invention to provide highly efficient surfactants for preparing microemulsions.
It is a further object to form microemulsions without the use of cosurfactants, which often add VOC's and objectionable odors.
It is a further object to provide compositions that are isotropic liquids over broad ranges of water content.
It is a further object to provide stable microemulsions that can be formulated with other surfactants, builders, and components common to cleaning formulations without destroying the microemulsion.